Multiferroic and nanomechanical properties of Bi1−xRxFeO3 polycrystalline films (R = La, Pr, Sm, and Ho; x = 0–0.15)

Abstract

We investigated phase constitutions, ferroelectric, magnetic, and nanomechanical characteristics of BiFeO3 films with rare-earth (R) substitution. Bi1−xRxFeO3 (R = La, Pr, Sm, and Ho; x = 0.05–0.15) thin film were prepared on the Pt buffered glass substrates by pulsed laser deposition. X-ray diffraction data indicated the occurrence of phase transition from rhombohedral structure to orthorhombic one in Bi1−xRxFeO3 thin films near x = 0.15, and an additional phase, Bi2Fe4O9, coexist for Bi1−xHoxFeO3 with x = 0–0.10. The studied BRFO polycrystalline films exhibit good ferroelectric and ferromagnetic properties at the same time. The remanent polarization (2Pr) of 77–164 μC/cm2 and electrical coercive field (Ec) of 310–493 kV/cm are obtained for BRFO films with R = La, Pr, Sm at x = 0.05–0.15 and R = Ho at x = 0.05. Good ferroelectric properties in BRFO films due to low leakage is highly related to phase constitution and interface morphology. Leakage mechanisms in BRFO films with various R and its contents x are also discussed. Besides, saturation magnetization (Ms) of 6.6–29.5 emu/cm3 and coercivity (Hc) of 125.0–549.4 Oe are obtained. The increased Ms with R and its contents x is related to the magnetic moment of the doped R3+ ion in addition to the suppressed spiral spin configuration. Finally, the hardness of 7.9–9.5 GPa for the BRFO films is found. The relationship between the hardness and grain size in good agreement with the Hall–Petch equation suggests the impeded propagation of dislocation by grain boundary mainly dominates the hardness. The result of this work indicates that the radius and magnetic moment of the R3+ ions plays a critical role in the structural evolution, refined microstructure, and therefore enhanced multiferroic and nanomechanical properties for rare-earth substituted BiFeO3 thin-film material systems.